Magnetic brush developing apparatus

ABSTRACT

A magnetic brush developing apparatus as disclosed having magnetic rollers with a driver member therewith and end sleeves formed of an insulating material. A trimming bar is provided having a concave portion below a leading edge thereof to facilitate the return to the sump zone of excess developing material. Magnets disposed within the rollers are mounted on channel members in a manner to direct the magnetic forces about each brush to ensure blanket coverage and a downstream configuration to direct developing material over a baffle associated with a cross-mixing baffle assembly. A screen is provided within the housing of the assembly to collect foreign objects. A mixing and transport device is positioned within the sump zone and is comprised of a plurality of spaced-apart augurs disposed on a shaft and a plurality of radially-extending bars affixed to the ends of the augurs.

United States Patent [191 Charland et al. I

[ MAGNETIC BRUSH DEVELOPING APPARATUS [75] Inventors: Terrence D.Charland, Pittsford;

Stanley D. Klett, Fairport, both of N.Y.

[73] Assignee: Xerox Corporation, Stamford,

Conn.

[22] Filed: Feb. 13, 1974 [21] Appl. No.: 442,036

Related US. Application Data [63] Continuation-impart of Ser. No.255,721, May 22,

1972, abandoned.

[56] References Cited UNITED STATES PATENTS Caudill 118/637 1 Sept. 23,1975 Primary Examiner-Morris Kaplan [57] ABSTRACT A magnetic brushdeveloping apparatus as disclosed having magnetic rollers with a drivermember therewith and end sleeves formed of an insulating material. Atrimming bar is provided having a concave portion below a leading edgethereof to facilitate the return to the sump zone of excess developingmaterial. Magnets disposed within the rollers are mounted on channelmembers in a manner to direct the magnetic forces about each brush toensure blanket coverage and a downstream configuration to directdeveloping material over a baffle associated with a cross-mixing baffleassembly. A screen is provided within the housing of the assembly tocollect foreign objects. A mixing and transport device is positionedwithin the sump zone and is comprised of a plurality of spaced-apartaugurs disposed on a shaft and a plurality of radiallyextending barsaffixed to the ends of the augurs.

3 Claims, 10 Drawing Figures US Patent Sept. 23,1975 Sheet 1 of53,906,898

US Patent Sept. 23,1975 Sheet 2 of5 3,906,898

US Patent Sept. 23,1975 Sheet 3 01 5 3,906,898

w w m S. Mm m US Patent Sept. 23,1975 Sheet4 0f5 3,906,898

US Patent Sept. 23,1975 Sheet 5 of5 3,906,898

MAGNETIC BRUSH DEVELOPING APPARATUS This is a continuation in part ofapplication Ser. No. 255,721, filed May 22, 1972, now abandoned.

BACKGROUND OF THE INVENTION This invention relates to improvements indeveloping apparatus for electrostatic printing machines, and moreparticularly, to improvements in a magnetic brush developing apparatusfor accomplishing highly efficient, fast speed development of anelectrostatically formed image.

In the practice of xerography as described in U.S. Pat. No. 2,297,691 toChester F. Carlson, a xerographic surface comprising a layer ofphotoconductive insulating material affixed to a conductive backing. isused to suppot electrostatic images. In the usual method of carrying outthe process, the xerographic plate is electrostatically chargeduniformly over its surface and then exposed to a light pattern of theimage being reproduced to thereby discharge the charge in the areaswhere light strikes the layer. The undischarged areas of the layer thusform an electrostatic charge pattern in conformity with theconfiguration of the original pattern.

The latent electrostatic image may then be developed by contacting itwith a finely divided electrostatically attractable material, such as aresinous powder. The powder is held in the image areas by theelectrostatic fields on the layer. Where the field is greatest, thegreatest amount of material is deposited; and where the field is least,little or no material is deposited. Thus, a powder image is produced inconformity with the image of the copy being reproduced. The powder issubsequently transferred to a sheet of paper or other transfer memberand suitably affixed to thereby form a permanent print.

The latest concept for Copiers utilizes high speed flash-exposure of adocument and the arrangement of a moving photoconductive material in theform of an endless belt which is continuously charged. Additionally,such copiers are provided with a developing system which supplies tonerparticles in relatively large quantities for solid area coverage, suchas a magnetic brush developing apparatus.

The electrostatically attractable developing material commonly used inmagnetic brush developing apparatus comprises a pigmented resinouspowder referred to here as a toner' and a carrier of larger granularbeads formed with steel cores coated with a material removed in thetriboelectric series from the toner so that a triboelectric charge isgenerated between the toner powder and the granular carrier. Themagnetizable carrier also provides mechanical control for the formationof brush bristles by virtue of magnetic fields so that the toner can bereadily handled and brought into contact with the exposed xerographicsurface. The toner is then attracted to the electrostatic latent imagefrom the carrier bristles to produce a visible powder image on aninsulating surface of the photoconductive material. Generally, in anendless belt printing machine configuration which employs a plurality ofmagnetic brushes, the brushes are arranged for'developing purposes witha run of the belt in the planar orientation.

In copending application Ser. No. 97,856, now U.S. Pat. No. 3,724,422,issued on Apr. 3, 1973 to Salvatore Latone and Michael R. Stanley,entitled Magnetic Brush Developing Apparatus, and assigned to the sameassignee, there is described a magnetic brush developing assemblycomprised of a plurality of magnetic brushes having their axes arrangedin parallel and in a plane generally parallel to the inclined plane ofthe photoreceptor belt at the zone of development therefor. The brushesare arranged so that the developing material in bristle form is moved inthe inclined plane, whereupon, after moving past the last brush in thestring of brushes, the material is returned for reuse to the sump at thebeginning end of the string by gravity forces.

In order to improve homogeneity of the developing mixture and preventtoner particle depletion in any zone of the apparatus, a cross-mixingbaffle assembly is provided, such as described in copending applicationSer. No. 97,688, now U.S. Pat. No. 3,697,050, issued on Oct. 10, .1972to Michael R. Stanley, entitled Cross-Mixing baffle, and assigned to thesame assignee. In the lower portion of the sump of the developingapparatus, a paddle wheel impeller is provided to transport developingmaterial towards the area adjacent the first magnetic brush of themagnetic brush developing apparatus.

In the magnetic brush developing apparatus heretofore used, arcing atvarious locations occurred which constituted a potential hazardoussituation, as well as to effect the charge on the photoconductivesurface thereby effecting the quality of the resulting image on atransfer member. Additionally, the developing material in the sump zonehas suffered from lack of homogeneity, especially when a plurality ofcopies are being produced having large selected portions of solid areacoverage. The relative positioning of the magnets within the rollers ofthe magnetic brush developing apparatus has resulted in the piling-up ofdeveloping material in undesirable locations within the housing withconcomitant excessive clean-up requirements. Still further, caking ofdeveloping materials has occured about the trimming bar configurationsheretofore employed.

OBJECTS OF THE INVENTION An object of this invention is to provide animproved magnetic brush developing apparatus.

Another object of this invention is to provide an improved magneticbrush developing apparatus wherein arcing is minimized therebyeliminating the necessity of insulating the magnetic brush developingapparatus from the frame of the electrostatic copier machine.

Still another object of the invention is to provide an improved magneticbrush developing apparatus having an improved mixing and transportdevice in the sump zone to improve the homogeneity of the developmentmaterial.

A further object of the invention is to provide an improved magneticbrush developing apparatus having an improved trim bar to minimizecaking about the area 1 of formation of the magnetic brush.

A still further object of the invention is to provide an improvedmagnetic brush developing apparatus wherein the quantity of toner addedto the developing material is more efficaciously monitored.

Still another object of the invention is to provide an improved magneticbrush developing apparatus including means for removing foreign objectsinadvertently introduced with make-up toner which could deleteriouslyeffect operation of the machine as well as the machine, per se.

SUMMARY OF THE INVENTION These and other objects of the invention areobtained in a magnetic brush developing apparatus by providing magneticrollers therefor having end sleeves formed of an insulating material,such as Teflon (a trademark of DuPont), and wherein the drive sprocketfor such rollers are formed from an insulating material, such as Nylon(a trademark of DuPont). A trimming bar is provided having a lead edgefor trimming the bristles forming on the proximate brush of the magneticbrush developing assembly and having a concave portion below suchleading edge to facilitate the return to the sump zone of developmentmaterial removed by the trimming bar. The trimming bar is mounted in aninsulating holder formed of a material, such as polypropylene, whichholder is affixed to the housing of the magnetic brush developingapparatus, as more fully hereinafter discussed.

The magnets disposed within the rollers of the apparatus, such asdescribed in copending application Ser. No. 220,965,now US. Pat. No.3,823,688, issued on July 16, 1964 to Stanley Klett, entitled MagneticBrush Assembly, assigned to the same assignee, are mounted on channelmembers in a manner to direct the magnetic forces about each brush toinsure blanket coverage and a downstream configuration to direct moreefficaciously the development material over a baffle associated with thehereinbefore mentioned cross-mixing baffle assembly. A screen isdisposed beneath the discharge conduits of the cross-mixing baffle tocollect foreign objects which may be readily removed during anyturn-around period of the machine. A mixing and transport device ispositioned within the sump zone of the apparatus and is comprised of aplurality of spaced apart augurs disposed on a shaft and a plurality ofradially extending bars affixed to the ends of the augurs to improve thehomogeneity of developing material.

DESCRIPTION OF THE DRAWINGS A better understanding of the presentinvention as well as other objects and further features thereof willbecome apparent upon consideration of the following detailed disclosurethereof, especially when taken with the accompanying drawings, whereinlike numerals designate like parts throughout.

FIG. 1 is a schematic sectional view of an electrostatic reproductionmachine embodying the principles of the invention;

FIG. 2 is a partial sectional view of the magnetic brush developingapparatus, in part, taken along the lines 2-2 of FIG. 4;

FIG. 3 is an elevational view of the other side of the magnetic brushdeveloping assembly shown in FIG. 2 and illustrating the drive mechanismfor the magnetic brush roller apparatus;

FIG. 4 is a top plane view of the roller assembly for a magnetic brushdeveloping apparatus;

FIG. 5 is a partial sectional view of the proximate roller of the rollerapparatus;

FIG. 6 is a cross-sectional view of an intermediate roller taken alongthe lines 66 of FIG. 4;

FIG. 7 is an enlarged cross-sectional view of the ultimate roller of themagnetic brush roller apparatus taken along the lines 7-7 of FIG. 4;

FIG. 8 is a front view of the mixing and transport device included inthe magnetic brush developing apparatus;

FIG. 9 is a top plane view of the magnetic brush roller assembly shownin FIGv 4, showing the relationship of the brush rollers to thereproduction machine photoconductive belt; and

FIG. 10 is an enlarged sectional view of the developing apparatustrimming blade assembly.

For a general understanding of the illustrated copier/reproductionmachine in which the invention may be incorporated, reference is had toFIG. 1 in which the various system components for the machine areschematically illlustrated.

A document D to be copied is placed upon a transparent support platen Pfixedly arranged in an illumination assembly, generally indicated by thereference numeral 10, positioned at the left end of the machine. Lightrays from an illumination system are flashed upon the document toproduce image rays corresponding to the informational areas. The imagerays are projected by means of an optical system onto the photosensitivesurface of a xerographic plate in the form of a flexible photoconductivebelt 12 arranged on a belt assembly, generally indicated by thereference numeral 14.

The belt 12 comprises a photoconductive layer of selenium which is thelight receiving surface and imaging medium for the apparatus, onaconductive backing. The surface of the photoconductive belt is madephotosensitive by a previous step of uniformly charging the same bymeans of a corona generating device or corotron 13.

The belt is journaled for continuous movement upon three rollers 20, 21and 22 positioned with their axes in parallel. The photoconductive beltassembly 14 is slidably mounted upon two support shafts 23 and 24, withthe roller 22 rotatably supported on the shaft 23 which is secured tothe frame of the apparatus and is rotatably driven by a suitable motorand drive assembly (not shown) in the direction of the arrow at aconstant rate. During exposure of the belt 12, the portion exposed isthat portion of the belt running between rollers 20 and 21. During suchmovement of the belt 12, the reflected light image of such originaldocument positioned on the platen is flashed on the surface of the beltto produce an electrostatic latent image thereon at exposure station A.

As the belt surface continues its movement, the electrostatic imagepasses through a developing station E in which there is positioned amagnetic brush developing apparatus, generally indicated by thereference numeral l5, and which provides development of theelectrostatic image by means of multiple brushes as the same movesthrough the development zone, as more fully hereinafter described.

The developed electrostatic image is transported by the belt to atransfer station C whereat a sheet of copy paper of transfer member ismoved between a transfer roller and the belt at a speed in synchronizmwith the moving belt in order to accomplish transfer of the developedimage solely by an electrical bias on the transfer roller. There isprovided at this station a sheet transport mechanism, generallyindicated at 17, adapted to transport sheets of paper from a paperhandling mechanism, generally indicated by the reference numeral 18, tothe. developed image on the belt at the station C.

After the sheet is stripped from the belt 12, it is conveyed into afuser assembly, generally indicated by'the reference numeral 19, whereinthe developed and transferred xerographic powder image on the sheetmaterial is permanently affixed thereto. After. fusing, the finishedcopy is discharged from the apparatus at a suitable point for collectionexternally of the apparatus. The toner particles remaining as residue onthe developed image, background particles and those particles otherwisenot transferred are carried by the belt 12 to a cleaning apparatus 26positioned on the rim of the belt between rollers 20 and 22 adjacent acharge device 25. Further details regarding the structure of the beltassembly 14 and its relationship with the machine and support thereformay be found in the copending Application Ser. No. 102,312, assigned tothe same assignee, now U.S. Pat. No. 3,730,623, issued on Jan. 5, 1973.

Referring first to FlGS. 2 and 5, particularly FIGS. 4 and 5, there isillustrated a roller assembly, generally indicated as 30, comprised ofend plates 32 and 34 which receive rollers 36, 38, 40, 42 and 44 andprovided with a plurality of holes (not shown) for mounting the rollerassembly 30 within the magnetic brush developing apparatus of themachine.

The roller 36 is comprised of a cylindrical sleeve 46 of a roughenedsurface formed of a non-magnetizable material and extending almost thelength of the housing of the developing apparatus 15. End sleeves 48,formed of an insulating material, such as Teflon (a trademark ofDuPont), are suitably disposed on the cylindrical sleeve 46 such as by aheat treatment whereby the sleeves 48 shrink about the ends of theroller 36. One end of the sleeve 46 is closed by a cap 50 which supportsa drive shaft 52 in coaxial alignment with the sleeve 46. The other endof the sleeve 46 is closed by a cap 54 having an orifice 56 throughwhich extends a shaft 58. Suitable bearing means 60 and 62 are providedon the shaft 58 which cooperates with inner bearing surfaces formed inthe end caps 50 and 54, respectively, to permit the sleeve 48 to rotateabout shaft 58. Within the sleeve 46, there are positioned elongated barmagnets 120, 122 (see FIG. 2), as more fully hereinafter discussed,extending nearly the full length of the sleeve 46 and suitably affixedto the shaft 58, such as by welding.

Rollers 38, 40, 42 and 44 are comprised of cylindrical sleeves 82 of aroughened surface formed of non-magnetizable material and co-extensivewith sleeve 46 of the roller 36, and are provided with end sleeves 84,similar to the end sleeves 48 of roller 36. One end of the sleeve 82 isclosed by a cap 86 which supports a drive shaft 88. The other end of thesleeve 82 is closed by a cap 90 having an orifice 92 through whichextends a shaft 94. Suitable bearing means 96 and 98 are provided on theshaft 94 which cooperate with inner bearing surfaces formed in caps 86and 90, respectively, to permit the sleeve 92 to rotate about the shaft94. Within the sleeve 82 there ispositioned an elongated bar magnet 126,as more fully hereinafter described, extending nearly the full length ofthe sleeve 82 and suitably affixed to the shaft 94.

The drive shafts 52, 88 of the rollers 36, 38, 40, 42 and 44 aresuitably mounted in bearings in end plate 32. The ends of the driveshafts 52and 88 of the roller 36, and the rollers 38 and 44,respectively, extending beyond the end plate 32 are provided withsprockets 96 and 98 respectively. The drive shafts 88 for rollers 40, 42are provided with sprockets 100, 102 respectively. Sprockets 96, 98,100, 102 are suitably affixed to their respective drive shaft, such asby pins 104. The sprockets are formed of an insulating material, such asNylon (a trademark of DuPont).

Referring specifically to FIGS. 2 and 3, the magnet roller assembly 30is disposed within the magnetic brush developing assembly 15 comprisedof a housing, generally indicated as 110, having a generally rectangularcross section and a length extending beyond the width of thephotoconductive belt 12. The housing is substantially closed except foran opening adjacent the photoconductive belt 12 whereat development ofthe latent image is effected. The housing 110 serves as a container,closed at its side, by end walls 1 12 and 114 and supporting an inclinedbottom wall 116 for containing developing material comprising carrierbeads from magnetizable material and colored electrostatic tonerparticles which adhere thereto.

As hereinabove discussed, the magnetic rollers 36, 38,40, 42 and 44 aremounted for rotation Within the housing 110 with their axes parallel andbelow the selenium belt 12. Within sleeve 46 of roller 36, there isprovided an angle bar 118 extending nearly the full length of the sleeve46 on which are mounted elongated bar magnets 120 and 122 with the frontsurface of bar magnet 120 being substantially parallel to the belt 12.The bar magnet 122 provides a means for transporting developing materialfrom the lower sump portion of the housing 116 adjacent the periphery ofsleeve 46 of the roller 36.

Within each sleeve 82 of the rollers 38, 40 and 42, a U-shaped channelmember 124 is mounted on each of the shafts 58 extending nearly the fulllength of the sleeves with elongated bar magnets 126 being affixed tothe outer surface of the innerly member extending between the outer legsof the U-shaped channel member 124 (see FIG. 6). The surface of barmagnets 126 of rollers 38 and 40 are substantially parallel to thesurface of the photoconductive belt 12. The surface of bar magnet 126 ofsleeve 42 is disposed at an angle of about 15 with the plane of thesurface of the belt 12. As seen in FIG. 7, the roller 44 is providedwith a generally S-shaped support member 128 mounted on the shaft 94 andextending nearly the full length of the sleeve 82. An elongated barmagnet 126 is mounted on the middle portion thereof with the surface ofthe magnet 126 being disposed at an angle of about 30 with the plane ofthe surface of the belt 12.

As shown in FIGS. 2 and 4, the peripheral walls of the roller 36 andthose for the other rollers are relatively close to each other. During adevelopment cycle when all rollers are rotating in unison in the samedirection and with their respective magnetic bars held stationary, thebrush bristles produced by the influence of the magnetic field emanatingfrom the bar magnets acting upon the magnetizable carrier beads in thedeveloping material will form on the upper region of the sleeve 36between this cylinder and the undersurface of the selenium belt 12.Bristles remain formed during the developing cycle, being initiated bythe influence of the bar magnet 122 disposed within sleeve 46 of theroller 36, and being maintained during rotation of the sleeve 46 by themagnetic field of the magnet 120. When the bristles are moved out of theinfluence of the magnet 120 of the roller 36 beyond the closest distancebetween the I belt 12 and the sleeve 46 thereof, bristle formation ismaintained by the influence of the magnetic field for the magnet 126associated with the sleeve 82 of the roller 38, which influence isstronger at this point than the diminished strength of the magneticfield attributed to the magnets 120 and 122 of the roller 36. Thisphenomenon is repeated until the last roller 44 is reached whereupon thedeveloping material is eventually returned to the sump zone via thehereinabove mentioned chute assembly.

During movement of the carrier beads and toner through the developmentzone B, the magnetic bristles and, therefore, the development material,is in the form of a magnetic blanket" extending continuously over all ofthe brushes of rollers 36, 38, 40, 42 and 44 for the entire width of thedevelopment zone B wherein the material is disposed or available to somedegree for developing purposes. It will be apparent that the width ofthe development zone B is larger than the sum of the individualdevelopment zones for each of the magnetic brushes. Further detailsregarding the formation and effect of the magnetic blanket" aredescribed in the copending application Ser. No. 830,285, assigned to thesame assignce, now US. pat. No. 3,640,248, issued on Feb. 8, 1972.

The relative positioning of the bar magnet 126 mounted on U-shapedchannel member 124 of roller 42 as well as the bar magnet 126 mounted onS-shaped member 128 of roller 44 results in a reduction of the magneticflux thereabout to facilitate release of toner particles attached to theroller 44 to direct more accurately the toner depleted developingmaterial to the hereinbefore described cross-mixing baffle assemblythereby minimizing build-up of developing material in undesirablelocations which would necessitate frequent cleanup. In the absence ofsuch configuration, the carrier particles have a tendency to adhere tothe rollers and flow down the reverse side of the brush assembly 30.

Also mounted for rotation within the development housing 116 and belowthe magnetic roller assembly 30, there is provided a mixing andtransport device, generally indicated as 130. Referring to FIG. 8, themixing and transport device 130 is comprised of a plurality ofspaced-apart augur elements 132 mounted on a drive shaft 134. Aplurality of radially extending flat bars 136 are mounted to the outerextending surface portion of the augur elements 132. Cylindricallyshapedcaps 138 and 140 are force fitted into the end portions of the bars 136.During a development cycle, the device 130 is caused to rotate in thedirection shown by the arrow in FIG. 2 and serves to mix developingmaterial within the zone defined by the augur elements 132 and totransport developing material by the flat bars 136 toward the pick-upzone adjacent the lower surface of the roller 36 independent of thestate of levelness and the amount of carrier beads in the system. Thedevelopment material in this vicinity is caused to be raised towards theroller 36 which will effect the formation of bristles on the sleeve 46of the roller 36. As this sleeve 46 is caused to rotate, the newlyformed bristles come under the influence of the magnet 120 and themagnetic blanket" for the assembly 17 is initiated. It is noted that theaugur elements 132 are disposed on the shaft 134 in a manner to permitlocalized intramixing of the developing material without conveyingdeveloping material from one end of the sump zone to another therebyminimizing localized concentration of developing material whileenhancing homogeneity thereof. v

. In order to optimize the length of the bristles during the formation.of the magnetic blanket" upon the sleeves, there is associated withroller 36 a trimming blade assembly, generally indicated as 142,extending the width of the housing 116 and secured to a lower bottomwall portion 144 of the housing 116 such as by bolts 145. The trimmingblade assembly 142 is comprised of a trimming blade 146 disposed withina mounting assembly 147 formed of an insulating material, such as athermoplastic resin, and is provided with an upper flat surface 148substantially tangential to the sleeve 36. The portion of the trimmingblade 146 extending towards the mixing and transport device isterminated in a knife'edge 149 formed by the intersection of the flatsurface 148 with a concave section 150 longitudinally formed in thetrimming blade below the surface 148 thereof. Such configurationeffectively determines the length of the bristles without the caking ofdeveloping material about the base thereof. The trimming blade 148 isspaced apart from the periphery of the roller 36 a short distance equalto the desired length of the bristles to be formed on the magnet brushassembly 30. It is noted that the trimming blade 146 does not directlycontact the housing 116 but is insulated therefrom by the plasticmounting assembly I47.

The rotational motion for all of the rotary components of the developingapparatus 15, is illustrated in FIG. 3, and is derived from a motor M-1and a drive system comprising, a sprocket 152 secured to a shaft of themotor, a smaller sprocket 154 also secured to the shaft, and timingchains 156 and 158 for connecting the sprockets 152 and 154,respectively, to the rotary components. Specifically, the chain 156 isdrivingly engageable with suitable sprockets 96 and 98, mounted on thedrive shafts 52, 88 of each of the rollers 36 and 38, respectively; anidler sprocket 158 formed of an insulating material, such as Nylon (atrademark of DuPont); and sprockets 102 and 98 secured to the driveshafts 88 of the rollers 42 and 44, respectively. A small chain 160 isprovided to connect sprocket 100 of roller 40 with sprocket 102 of theroller 42 (see FIG. 4) thereby simultaneously driving roller 40 which isnot directly connected to timing chain 156. With this arrangement, themagnetic brush rollers are rotated with the same peripheral speeds, inthe same direction in a direction which moves the magnetic blanket"comprising magnetic brush bristles upwardly in an inclined planearranged at the same angle as the angle of the plane of the belt in thedevelopment mode.

The timing belt 158 is connected to the drive sprocket 154 and with adriven sprocket 162 secured to the shaft 134 for the mixing andtransport device 130 thereby to assure that the device 130 and themagnetic brush sleeves rotate in unison. The relative speed of thedevice 130 is slightly less than the peripheral speeds of the magneticbrush sleeve but is provided with a surface capacity which provides anexcess of developing material being transported to the area about thesleeve 46 of the proximate roller 36.

The depleted developing material which is carried beyond the magneticbrush of roller 44 (the last brush in the series of magnetic brushesthat comprise the developing device) is returned to the housing 110 inorder to be re-used for development purposes. As the developing materialis moved by the cylinder 44 away from the development zone B, it isdirected by a longitudinal planar baffleplate 170 secured at its'ends tothe end walls 112 and 114 of the developer housing 116 to the upper endof a cross-mixing baffle assembl'yj ge-nerally indicated by the numeral172; Another baffle plate 174 is mounted on the planar baffle plate 170to direct representative portions of the depleted deiveloping materialthrough an automatic developer eontr ol, generally indicated as 176, tomonitor effectively the rate of toner depletion and therebyappropriately add toner from a supply reservoir, generally indicated as178, as warranted by the rate of toner depletion.

Disposed below the cross-mixing baffle assembly 172, there is provided agenerally U-shaped screen 1.80 suitably mounted to the back wall 116 ofthe housing 110 and extending the width thereof. The lower leg of thescreen is disposed within the housing 110 in a manner to classify andcollect any foeign objects, such as paper clips foreign the like whichmay be inadvertently introduced into the toner supply reservoir 178.

While the description of the present invention has been directed to amagnetic brush apparatus having five rollers, it should'be understoodthat less rollers, e.g., one roller, may be employed depending on the designed duty of the machine. Additionally, while the invention has beendescribed with reference to a machine having an endless photoconductivebelt assembly, it is understood that the principle of the invention isapplicable to a machine employing a photoconductor drum wherein one ormore rollers are provided in the magnetic brush assembly.

As best seen in FIG. 9, and as described heretofore, belt 12 comprises aphotoconductive layer of selenium, designated by the numeral 6, on aconductive backing, designated by the numeral 7. Normally, the extent ofthe photoconductive layer 6 is somewhat less than the extent of theconductive backing 7 leaving a bare edge portion 8 along each side ofthe conductive backing 7. Conductive backing 7 is suitably grounded asby means of brush 9.

The before described magnetic brush developing assembly 30 hasdeveloping rollers 36, 38, 40, 42, and 44 thereof disposed substantiallynormal to belt 12, the rollers 36, 38, 40, 42, and 44 being of a lengthsubstantially equal to or slightly greater than the width of belt 12.The insulating end sleeves 48, 84 are disposed opposite the bare edgeportions 8 to prevent shorting between the developing rollers 36, 38,40, 42, and: 44 and the conductive backing 7 of belt 12 as will appear.

In order to enhance development of the latent electrostatic images onbelt 12, the sleeves 46, 82 of developing rollers 36, 38, 40, 42, and 44are biased to a preselected voltage level from a suitable voltagesource, illustrated in exemplary fashion in FIG. 9 by battery 4. Thebias is applied to rollers 36, 38, 40, 42, and 44 via a commutator bar37 which is electrically connected to sleeve supporting shaft 58 ofroller 36 and shafts 94 of rollers 38, 40, 42, and 44. The conductivepath from the shafts 58, 94 may be traced through the sleeve bearingsuch as bearing 62 of developing roller 36 (see FIG. to the sleeveitself. A typical biasing voltage is 400 volts.

To prevent shorting or grounding of the biased developing rollers 36,38, 40, 42, and 44, with the adjoining components and parts, eitherdirectly. or through bridging Circuits established through thesemiconduetive carrier of the developing material, with possibledeterioration in the quality of the image developed, certain'of theoperating components are fabrieated from or supported through insulatingmaterials as described earlier. More specifically, sleeves 48, 84 whichare mounted on the terminal ends of developing rollers 36, and 38, 40,42, and 44, respectively are comprised of an insulating material and areof a size and disposition to prevent conduction between the biaseddeveloping rollers 36, 38, 40, 42, and 44 and the bare side edges 8 ofbelt 12. Similarly, the mounting assembly 147 for trimming blade 146 iscomprised of an insulating material to obviate shorting or grounding ofthe biased developing roller 36 via developing material trappedtherebetween. In like manner, the drive sprockets 96, 98, 100, 102, 158for developing rollers 36, 38, 40, 42, and 44 and the drive sprocket 162for mixing and transport device are formed from a suitable insulatingmaterial such as nylon to prevent shorting of the rollers 36, 38, 40,42, and 44 through the drive mechanism or through transport device 130.And, the baffle plates 170, 174 are electrically isolated from thehousing 116 to prevent shorting of developing roller 44.

The improved trimming blade assembly 142 which serves to optimize thelength of the bristles during the formation of the magnetic blanket uponthe sleeves of the developing rollers 36, 38, 40, 42, and 44 asdescribed earlier, reduces the torque load placed upon motor M-l,driving both rollers 36, 38, 40, 42, and 44 and mixing and transportdevice 142. This reduction in the power required to drive the developingcomponents in turn reduces the amount of heat generated, and hence thetemperature to which the developing material is exposed to promotecarrier life.

As seen best in FIG. 10, excess developing material picked up bydeveloping roller36 is trimmed off by the leading edge 149 of trimmingbar 148 to provide a preselected developing material blanket or pileheight. As the developing roller 36 rotates, the blanket of developingmaterial is drawn into the progressively decreasing throat or passage151 formed between the surface 148 and the periphery of roller 36 tocompact the developer blanket or pile prior to the developer blanketcoming into operative disposition with belt 12. In this manner, theheight of the developing material pile brought into operativerelationship with belt 12 by developing roller 36 is controlled while atthe same time a sufficient quantity of developing material is assuredfor the succeeding developing rollers 38, 40, 42, and 44.

While the instant invention as to its objects and advantages has beendescribed herein as carried in specific embodiments thereof, it is notdesired to be limited thereby; but it is intended to cover the inventionbroadly within the scope of the appended claims.

What is claimed is:

1. In a magnetic brush developing apparatus having at least one magneticbrush roller assembly for applying developer materials to aphotoconductive surface, said photoconductive surface being supported bya conductive substrate having at least one bare portion adjoining saidmagnetic brush roller assembly, the magnetic brush roller assemblyincluding a rotatable exterior sleeve with magnet means disposedtherewithin, and means to place a preset electrical bias on the rollerassembly to further development of electrostatic latent images on thephotoconductive surface, the improvement comprising:

means to prevent grounding of said roller assembly with adjoining partsof said developing apparatus and loss of said roller assembly bias,

said means to prevent grounding including an insulating ring on saidroller assembly exterior sleeve opposite said conductive substrate bareportion to prevent discharge of said roller assembly through saidconductive substrate.

2. In a magnetic brush developing apparatus having at least one magneticbrush roller assembly for applying developer materials to aphotoconductive surface, the magnetic brush roller assembly including arotatable exterior sleeve, magnet means disposed within said sleeve,means for journalling said roller assembly exterior sleeve for rotation,and means to place a preset electrical bias on the roller assembly tofurther development of electrostatic latent images on thephotoconductive surface, the improvement comprising:

means to prevent grounding of said roller assembly with adjoining partsof said developing apparatus and loss of said roller assembly bias, saidmeans to prevent grounding including drive means for rotating saidroller assembly exterior sleeve,

said drive means having a driven member rotatable in unison with saidsleeve and a driving member engageable with said driven member to rotatesaid driven member with said sleeve, said driven member being comprisedof electrically insulating material whereby to prevent discharge of saidroller assembly bias through said drive means.

3. In a magnetic brush developing apparatus having at least one magneticbrush roller assembly for applying developing materials to aphotoconductive portion of a conductive substrate, the magnetic brushroller assembly including a rotatable exterior cylinder with magnetmeans disposed therewithin, and means to place a preset electrical biason the roller assembly to enhance development of electrostatic latentimages in an electrostatic printing machine, the improvement comprising,means to prevent grounding engagement of said roller assembly cylinderwith nonphotoconductive portions of said substrate with consequentdeterioration of said cylinder bias, said last mentioned meanscomprising insulating sleeve members disposed on said roller assemblycylinder opposite said substrate non-photoconductive portions.

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1. In a magnetic brush developing apparatus having at least one magneticbrush roller assembly for applying developer materials to aphotoconductive surface, said photoconductive surface being supported bya conductive substrate having at least one bare portion adjoining saidmagnetic brush roller assembly, the magnetic brush roller assemblyincluding a rotatable exterior sleeve with magnet means disposedtherewithin, and means to place a preset electrical bias on the rollerassembly to further development of electrostatic latent images on thephotoconductive surface, the improvement comprising: means to preventgrounding of said roller assembly with adjoining parts of saiddeveloping apparatus and loss of said roller assembly bias, said meansTo prevent grounding including an insulating ring on said rollerassembly exterior sleeve opposite said conductive substrate bare portionto prevent discharge of said roller assembly through said conductivesubstrate.
 2. In a magnetic brush developing apparatus having at leastone magnetic brush roller assembly for applying developer materials to aphotoconductive surface, the magnetic brush roller assembly including arotatable exterior sleeve, magnet means disposed within said sleeve,means for journalling said roller assembly exterior sleeve for rotation,and means to place a preset electrical bias on the roller assembly tofurther development of electrostatic latent images on thephotoconductive surface, the improvement comprising: means to preventgrounding of said roller assembly with adjoining parts of saiddeveloping apparatus and loss of said roller assembly bias, said meansto prevent grounding including drive means for rotating said rollerassembly exterior sleeve, said drive means having a driven memberrotatable in unison with said sleeve and a driving member engageablewith said driven member to rotate said driven member with said sleeve,said driven member being comprised of electrically insulating materialwhereby to prevent discharge of said roller assembly bias through saiddrive means.
 3. In a magnetic brush developing apparatus having at leastone magnetic brush roller assembly for applying developing materials toa photoconductive portion of a conductive substrate, the magnetic brushroller assembly including a rotatable exterior cylinder with magnetmeans disposed therewithin, and means to place a preset electrical biason the roller assembly to enhance development of electrostatic latentimages in an electrostatic printing machine, the improvement comprising,means to prevent grounding engagement of said roller assembly cylinderwith non-photoconductive portions of said substrate with consequentdeterioration of said cylinder bias, said last mentioned meanscomprising insulating sleeve members disposed on said roller assemblycylinder opposite said substrate non-photoconductive portions.